According to known conventional technologies for a radio communication system, the travel speed of a communication terminal is detected based on a channel estimate (see, e.g., Japanese Laid-Open Patent Publication Nos. 2008-278076, 2008-300923, 2006-74265, and 2006-33207). For example, Japanese Laid-Open Patent Publication No. 2008-278076 discloses a technique of detecting reception levels of multiple known signals transmitted by a communication destination device in respectively different periods and acquiring propagation path variation information according to the result of comparison of a difference between reception levels detected for individual known signals with a threshold.
Another technique is known, according to which a mobile terminal controls transmission power based on a moving average of reception levels of pilot signals for multiple time slots from a base station (see, e.g., Published Japanese-Translation of PCT Application, Publication No. 2006/077647). Still another technique is known, according to which a printer calculates a moving average of multiple sample data of duty in order to reduce noise in duty information (see, e.g., Japanese Laid-Open Patent Publication No. H10-138594).
The above conventional techniques, however, pose a problem in that because the characteristics of a channel estimate to the travel speed of the mobile radio device vary depending on the band of a reception signal, the travel speed cannot be determined precisely even if the variation of the channel estimate is compared with a threshold.